Microfluidics has developed greatly in recent years and monolithic elastic polymer, such as polydimethylsiloxane (PDMS), microfluidic chips are now an enabling technology for creating many high throughput assays. Recently, microfluidic devices fabricated from PDMS using soft lithography have seen widespread use in biology and chemistry. This technology permits inexpensive fabrication and integration of fluidic circuit elements such as channels, valves, and pumps. This development of integrated microfluidic devices has enabled the large-scale integration of biological assays on a single device, often termed lab-on-chip (LOC). Such devices have found important applications in areas including immunology, stem cell culture, and structural chemistry. These systems can perform hundreds of automated assays in parallel, thus reducing operation time and reagent volume. Over the last ten years, PDMS has emerged as the material of choice for many microfluidic systems because of its low cost, ease of fabrication and biological compatibility. Monolithic PDMS membrane valves enable both the sequencing of reagent/reactant flow control structures directly onto PDMS devices. With the increase in the number of flow control operations on a single chip an increase in the number of signal connections are required for control and sequencing. Because of their symmetry, PDMS membrane valves inherently have a pressure gain of less than one, where a lower pressure line cannot be used to control a higher pressure one. This significantly limits membrane valve logic structures to a single level of logic. As a result, many control signals need to be chip inputs driven externally from a higher-pressure source. What is needed is a low-cost valve with pressure gain, where a lower-pressure port controls a higher-pressure port, to enable digital control logic to be built on-chip to reduce external signal counts.
Numerous approaches have achieved pressure gain using materials in addition to or in lieu of PDMS, including Silicon valves and glass-PDMS valves. Unfortunately, the additional cost, required equipment, and complexity of working with other materials has limited the adoption of these valves to logic technologies for highly integrated LOCs.
Valves made with conventional PDMS soft lithography tend to require a control pressure greater than the pressure in the line being controlled to turn the value off, where the pressure gain of the valve is less than one. Other PDMS soft lithography valves currently provided are actuated using vacuum or magnetic drive sources.
Accordingly, there is a need to develop a valve exhibiting pressure gain that can be easily implemented in the standard PDMS planar process. Such a valve would allow static logic gates to be built directly on chips using soft lithography.